Bituminous mastic



Patented Oct. 16, 1928.

- UNITED STATES PATENT OFFICE.

' CHARLES N. FORREST AND JOHN' STROTHER MlLLER, JR., OF RAHWAY,' NEW JERSEY, I

AND CHARLES S. BAIBB, OF QHICAGO, ILLINOIS, ASSIQNORS TO THE BARBER AS- PHALT COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF'WES'll VIRGINIA.

N6 Drawing. I

Our invention relates to improvements in bituminous mastics for use as a weather andwearing surface for floors, walks and light driveways.

Bituminous mastic has been known and used for many years as a weather and wear- 'lng surface for roofs, floors,'foot walks and light driveways. It is composed essentially of a graded mineral aggregate and a bituminousbinder, andis distinguished from the bituminous wearing surface of streets and roadways by containing so much of the bituminous binder that when hot it is of dough-- like consistency so that it can be compressed and smoothed to a true surface with light hand tools such as a wood float or spatula. On the other hand, the bituminous wearing surface of the streets and roadways is com paratively lean in bituminous binder and even when hot is still of a granular and relatively dry appearance and condition. It is spread with rakes as a loose mixture and afterwards compressed with heavy mechanically operated rollers, weighing from 5 to 1.0 tons. As bituminous mastic is used inbuildings as a floor surface or overlight foundation course as in a park or sidewalk or light driveway, it must necessarily be of such a nature that it can be put in place without a heavy roller, as is the'practice in compressing bituminous street paving surfaces.

The presence in bituminous mastic. of a surplus of bituminous binder (over what would be suiiicient to hold the mineral aggregate together and form a watertight surface) has constituted a defect in such mastic making it more or less plastic, and when heavy loads, or even moderate loads supported upon but a small area. are placed upon it, they sink into and markby indentations the floor or walk to an objectionable degree, making it unsightly and rough.

Bituminous, mastic has heretofore been made in two ways. The first and earliest way is to select and pulverize a native rock as-' phalt, usually and preferably a calcareous rock which is of a porous nature and has become impregnated through natural causes with a maltha or other form of native bitumen. Such rock carries from 5 to 10% bitupulverized and even when heated does not ,BI'rUMmo'us MASTIC. I

Application filed my 12, 1922. Serial No. 574,546.

becomesufliciently plastic to be used alone as mastic. The pulverized bituminous rock is therefore heated and enriched with additional pure bitumen so as to be made more plastic.

The other and second way to make bituminous mastic, and this has been the method for making it up to the present time, is to take pulverized limestone, silica, or other rock dust and to combine it under heat with enough bitument to produce a plastic composlt on. I

By following either one or the other of the foregoing methods a material known in the art as masticcake has been produced. Such cake usually contains about 15% bitumen and about 85% pulverized rock, which is so 7 finely ground that some 75% of it or more will pass through a 200 mesh sieve (A. S. T.- M. standard).

\Vhen a bituminous mastic floor or other surface is to be constructed, such mastic cake is placed in a melting pot over a fire along withaddit-ional bitumen and a quantity of graded, coarse gravel, sand or stone screenings, and the entire 'mass heated and stirred together until a homogeneous mixture is pro: duced, which'has the-working qualities desired and hereinbefore described. It is then spread and worked into place with hand tools to a depth of about one inch. The usual working formula for the final mixture is approximately 700 lbs. mastic cake.

. 700 lbs. coarse sand or gravel.

7 0 lbs. additional bitumen.

By analysis, such mixtures show approximately Per cent.

Bitumen 10 tol2 200 mesh stone dust 20 to 30 Graded coarse sand from '8 to 100 mesh (coarse particles predominating) 68 to 70 The above type of mixture has been in common use for many yearsand-was developed in 100 principles of either As previously stated, such mastic has the serious defect of too great plasticity to be entirely satisfactory, which defectais due to the excess of bitumen which has been necessitated on'the one hand by the requirement of manipulation with light hand tools, and on the other by the large amount of fine stone dust required to provide adequate surface area to carry said excess of bitumen.

We have discovered that a superior bituminous mastic can he prepared by departing radically from the practices heretofore tollowedin this art. utilizing, in the first place, sand or crushed rock particles, ungraded' and preferably all of one size, although in practice this is impossible on account of cost, and we utilize such particles of substantially one size as our mineral aggregate. The reason for this is because a unit volume of substantially one size particles or grains keys together into a more stable mass than the graded sands of commerce. For instance-we employ amass of particles which Will all pass through a 10 mesh sieve and be retained upon a 30 mesh sieve, as this kind is commercially available, but any narrow group of particles finer than 8 mesh and coarser than 60 mesh will answer as long as such provide when ultimately compacted not less than 30% voids. A mass of particles of essentially one size will contain a larger percentage of voids than a mass of graded particles. Vi e do not utilize any stone dust in our mineral aggregate, although there is no disadvantage in the presence of a small amount of such dustsay up to 5%, and accidental contamination by such a quantity as that can scarcely be avoided in commercial practice.

Instead of using stone dust to fill the voids in our sand aggregate, we employ a fine fibrous flock or flock-powder, as it is also termed.

\Ve find that this has a greater capacity for carrying bitumen than stone dust and does not lubricate the particles of the mineral aggregate as stone dust does, We prefer asbestos or other mineral flock, because this will withstand the heat employed in the preparation of our mixture better than organic fibres, but wedo not confine ourselves to asbestos or other mineral flock, as cotton, wool or other organic fibres may, under some circumstances, be employed especially when asbestos or other mineral flock is difficult or impossible to obtain.

By asbestos flock will be understood the short individual fibres of asbestos, not the asbestos threads of commerce which are made up of a mass of individual fibres. We may pass such asbestos threads of commerce shredding mill which tears them apart and thus increases the bulk of the mathrough a terial two or three fold. I

The exact amount of asbestos flock employed depends somewhat upon the size of the Our departure consists in as a binder,

particles of mineral aggregate, but this is small in weight in any event-not exceeding 2 of the aggregate.

Such a combination of mineral aggregate and asbestos flock will then carry from 13% to 16% bitumen, and produce a desirable mixture bothfrom the point 'of view of being suificiently plastic .at temperatures between 300 F. and 400 F. to be placed and spread to a smooth surface with hand tools, and of being so stable at all atmospheric temperatures as to bear heavy loads without indentation or displacement. The asbestos flock makes possible the use of larger quantities of bitumen without loss of stability, than would otherwise be the case, and this increase of bitumen adds to the waterproofing, non-cracking and Formerly the bitumen and stone dust were placed in a fire heated kettle equipped with revolving stirring arms and slowly manipulated for several hours until all became heated and mixed. We do not employ dust, which would all be blown away if heated in the revolving driers of the type available for such' work. "We utilize a revolving sand heater or dryer, set in a furnace, similar to those employed in preparing bitumen street paving mixtures. Our sand is fed to such a drier continuously and heated to about 450 F. As

it leaves the drier, it passes over a revolvlngscreen to classify the size of particles and falls through this screen into a hopper. From the hopper it is weighed out by suitable scales and dumped into a pug mill which is also of the type used in the preparation of bituminous street paving mixtures.

Our bitumen which may be asphalt of any kind, coal tar pitch or the equivalent of either is melted and heated in any suitable manner to about 350 F. and kept in quantity as wanted. It is weighed or measured as desired for. each batch. Our asbestos flock is prepared in advance and placed in suitable containers in suflicient quantity to introduce directly into each batch of mixture. Having thus provided our raw materials, we place say 750 lbs. of heated and selected sand in the revolving pug mill,'the'n add say 6 lbs. of unheated asbestos flock. These are mixed together for about one minute so as to thoroughly distribute the flock in the hot sand and to heat it. We then add say 244 lbs. of melted Trinidad asphalt cement which has been already tempered to the desired c0nsistency and continue the mixing operation for another minute. If we are using an asphalt which is pure bitumen (the Trinidad asphalt will contain but about 62% bitumen) the sand is increased to about 843.5 lbs., the asbestos flock to 6.5 lbs. and the asphalt decreased to about 150 lbs. Aspreviously described, the proportions of the mixture will necessarily have to be varied somewhat to suit the specific raw material employed, but in any event the finished product will be understood to be such that it will contain from 13 to 18% bitumen and from'% to 1%% asbestos or other fibrous flock and an ungraded aggregate of mineral particles or grains such as sand, essentially of one size but all smaller than 8 mesh. Accordingly, the proportions of flock to bitumen will lie between about 2.8% and 13.5%.

By our method of'procedure as just described, we are ableto produce a batch of finished mixture in from two to three minutes, compared with several hours usually 6 0r 8, for the former typev of mixture and method employed in its manufacture.

Having completed a batch of mixture as thus described, it may be laid at once as a 'floor surface, but is usually dumped out into molds of conventional size and shape and cooled by plunging the units thereof into water or standing them aside in the atmosphere. Our mastic as'just described does not have to be combined subsequently with additional bitumen and sand as does the present mastic. On the contrary, it would be spoiled and rendered unfit if it were, and much advantage resides in the.fact that it can be prepared in large quantity at a central plant where proper laboratory supervision is economically possible, and sent to the work at a distance requiring nothing more there than reheating and putting it in place. This possibility permits of great economy in the construction of floors because of less labor in handling one thing instead of three, less fire in drying wet gravel on the ob and fewer melting pots. When our mastic arrives on the job, the cakes are broken apart roughly with an axe and placed in a fire heated kettle along with a little free water. As the water boil its heat and steam softens the cakes and prevents their burning, where in direct contact with the kettle bot- .tom, and thus facilitates the remelting operation as a shop expedient.

.While we have dwelt especially upon the availability of our mastic as the wearin surfaceof floors and walks, it is equally avallable for use as alining for reservoirs, swimming pools and tanks for the purpose of rendering them watertight.

claim:

v June,- 1922. Having thus described our invention, we

aggregate" ofessentially'one size grains, the.

size being between the limits of eight and sixty mesh screens, 13% to 18% of bitumen,

and .5% to 1.75% of fibrous flock. 1

3. A bituminous mastic including a mineral aggregate which when compacted has at least 30% of voids, and mixed bitumen and fibrous flock within said voids, the ratio of the per centage of fibrous flock to that of the aggregate being between .005 and .025.

4. A bituminous mastic including a mineral aggregate, the grains of whlch are between I the limits of eight and sixty mesh screens, bitumen, and fibrous flock, the ratio of the percentage of fibrous flock to that of the aggregate being between .005 and .025. 5. A bituminous masticiincluding amineral aggregate, the grains of which are between the limits of eight and sixty mesh screens, bitumen and fibrous flock, the ratio of the percentage of fibrous flock to that of bitumen being between .028 to .135.

6, A bituminous mastic including a mineral aggregate which when compacted has at least 30% of voids, and mixed'bitumen and fibrous flock within said voids, the ratioof the percentage of fibrous flock to that of bitumen being between .028 and .135.

7. A bituminous mastic including a mineral aggregate, bitumen and fibrous flock, the ratio of the percentage of fibrous flock to that of bitumen being between .028 and .135.

'8. A bituminous mastic including 84% to 85% of a mineral aggregate the grains of which are between the limits of eight and sixty mesh screens, 14% to16% of bitumen, and .6 to .7 %of fibrous flock.

\ In testimony whereof, we, the said .CHARLES N. FORREST and JOHN STROTHER MILLER, J12, have hereunto signed our names at Philadelphia, Pennsylvania, this 29th day of June, 1922.

CHARLES N. FORREST. JOHN STROTHER MILLER, JR. In testimony whereof, I, the said CHARLES S. BABB, have hereunto signed my name at Philadelphia, Pennsylvania, this 29th day of CHARLES s. BABB. 

